feature #15185 Implement resettable containers (stof)

This PR was merged into the 2.8 branch.

Discussion
----------

Implement resettable containers

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | small one
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #13448
| License       | MIT
| Doc PR        | n/a

This allows to release remove references to all services during shutdown, giving much more chances to destruct services and the container through refcounting rather than waiting GC, as it will break cycles between the container and container-aware services.

There is a small BC break for a very edge case: if someone keeps a reference to the container and then shutdowns the kernel, the container would now be cleared and so would not work as intended anymore. But I don't think it is a supported use case. If you shutdown the kernel, the container of this kernel is released by the kernel and should not be used anymore IMO.
Thus, shutting down the kernel generally does not happen except during tests on teardown.

I'm not sure a doc PR is needed here: users of the fullstack framework should never use this feature (the kernel is using it for them). What do you think @weaverryan ?

Commits
-------

4457745 Implement resettable containers

src/Symfony/Component/DependencyInjection/CHANGELOG.md

@@ -7,6 +7,7 @@ CHANGELOG
  * allowed specifying a directory to recursively load all configuration files it contains
  * deprecated the concept of scopes
  * added `Definition::setShared()` and `Definition::isShared()`
+ * added ResettableContainerInterface to be able to reset the container to release memory on shutdown
 
 2.7.0
 -----

src/Symfony/Component/DependencyInjection/Container.php

@@ -13,6 +13,7 @@ namespace Symfony\Component\DependencyInjection;
 
 use Symfony\Component\DependencyInjection\Exception\InactiveScopeException;
 use Symfony\Component\DependencyInjection\Exception\InvalidArgumentException;
+use Symfony\Component\DependencyInjection\Exception\LogicException;
 use Symfony\Component\DependencyInjection\Exception\RuntimeException;
 use Symfony\Component\DependencyInjection\Exception\ServiceNotFoundException;
 use Symfony\Component\DependencyInjection\Exception\ServiceCircularReferenceException;
@@ -60,7 +61,7 @@ use Symfony\Component\DependencyInjection\ParameterBag\FrozenParameterBag;
  *
  * @api
  */
-class Container implements IntrospectableContainerInterface
+class Container implements IntrospectableContainerInterface, ResettableContainerInterface
 {
     /**
      * @var ParameterBagInterface
@@ -375,6 +376,18 @@ class Container implements IntrospectableContainerInterface
         return isset($this->services[$id]) || array_key_exists($id, $this->services);
     }
 
+    /**
+     * {@inheritdoc}
+     */
+    public function reset()
+    {
+        if (!empty($this->scopedServices)) {
+            throw new LogicException('Resetting the container is not allowed when a scope is active.');
+        }
+
+        $this->services = array();
+    }
+
     /**
      * Gets all service ids.
      *

src/Symfony/Component/DependencyInjection/ResettableContainerInterface.php

@@ -0,0 +1,31 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\DependencyInjection;
+
+/**
+ * ResettableContainerInterface defines additional resetting functionality
+ * for containers, allowing to release shared services when the container is
+ * not needed anymore.
+ *
+ * @author Christophe Coevoet <stof@notk.org>
+ */
+interface ResettableContainerInterface extends ContainerInterface
+{
+    /**
+     * Resets shared services from the container.
+     *
+     * The container is not intended to be used again after being reset in a normal workflow. This method is
+     * meant as a way to release references for ref-counting.
+     * A subsequent call to ContainerInterface::get will recreate a new instance of the shared service.
+     */
+    public function reset();
+}

src/Symfony/Component/DependencyInjection/Tests/ContainerTest.php

@@ -320,6 +320,49 @@ class ContainerTest extends \PHPUnit_Framework_TestCase
         $this->assertTrue($sc->initialized('alias'), '->initialized() returns true for alias if aliased service is initialized');
     }
 
+    public function testReset()
+    {
+        $c = new Container();
+        $c->set('bar', new \stdClass());
+
+        $c->reset();
+
+        $this->assertNull($c->get('bar', ContainerInterface::NULL_ON_INVALID_REFERENCE));
+    }
+
+    /**
+     * @expectedException \Symfony\Component\DependencyInjection\Exception\LogicException
+     * @expectedExceptionMessage Resetting the container is not allowed when a scope is active.
+     * @group legacy
+     */
+    public function testCannotResetInActiveScope()
+    {
+        $c = new Container();
+        $c->addScope(new Scope('foo'));
+        $c->set('bar', new \stdClass());
+
+        $c->enterScope('foo');
+
+        $c->reset();
+    }
+
+    /**
+     * @group legacy
+     */
+    public function testResetAfterLeavingScope()
+    {
+        $c = new Container();
+        $c->addScope(new Scope('foo'));
+        $c->set('bar', new \stdClass());
+
+        $c->enterScope('foo');
+        $c->leaveScope('foo');
+
+        $c->reset();
+
+        $this->assertNull($c->get('bar', ContainerInterface::NULL_ON_INVALID_REFERENCE));
+    }
+
     /**
      * @group legacy
      */

src/Symfony/Component/HttpKernel/Kernel.php

@@ -23,6 +23,7 @@ use Symfony\Component\DependencyInjection\Loader\IniFileLoader;
 use Symfony\Component\DependencyInjection\Loader\PhpFileLoader;
 use Symfony\Component\DependencyInjection\Loader\DirectoryLoader;
 use Symfony\Component\DependencyInjection\Loader\ClosureLoader;
+use Symfony\Component\DependencyInjection\ResettableContainerInterface;
 use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\HttpFoundation\Response;
 use Symfony\Component\HttpKernel\Bundle\BundleInterface;
@@ -180,6 +181,10 @@ abstract class Kernel implements KernelInterface, TerminableInterface
             $bundle->setContainer(null);
         }
 
+        if ($this->container instanceof ResettableContainerInterface) {
+            $this->container->reset();
+        }
+
         $this->container = null;
     }